The present invention relates to a marked improvement over the acrylic silane resins used for coating compositions, and the process for making such resins, which were disclosed in U.S. Pat. No. 4,801,658, issued Jan. 31, 1989 to Furukawa et al. (hereinafter referred to as the '658 patent). The '658 patent discloses a curable resin having a hydrolyzable silyl group at the ends or side chains and having excellent flexibility, solvent resistance and adhesion to organic materials, and a process for preparing the curable resins.
A disadvantage of making the resin of the '658 patent is that their method of making oligomer (A) having in its molecule two or more acryloyl groups and/or methacryloyl groups (hereinafter referred to as "(meth)acryloyl group") leads to by-products or involves a multi-step synthesis.
When oligomer (A) is made in a one-step process (Ref. Examples 1, 3, and 8 of the '658 patent) both acrylyol containing hydroxy functional compounds and methacrylyol hydroxy functional compounds in a 2 to 1 ratio are used equimolar to the isocyanate of the bifunctional isocyanate containing compound. This inevitably leads to a product mixture of the desired oligomers having an acryloyl group and methacryloyl group at each end of the oligomer as well as the undesired by-product of oligomers with 2 acryloyl groups at each end of the molecule. When this product mix is subsequently reacted with the silane coupling agent (B) having active hydrogen (to form the hydrolysable silane functional prepolymer) the oligomers with two acryloyl groups on each end form unwanted bifunctional silanes with no vinyl unsaturation.
When oligomer (A) is made in a two-step process (Ref. Examples 4, 5, 6 and 7 of the '658 patent) a purer compound will be obtained. (In the two step process a methacryloyl reactive compound is first reacted with a difunctional isocyanate, and the resulting product is further reacted with an acryloyl fuctional product in an attempt to obtain an oligomer with both acrylolyl and methacryloyl functionality). The problem with this approach, however, is that difunctional telechelic products will be formed since the difference in reactivity between the two isocyanate groups is too small to be selective.
What is needed is a simplified one-step process of making an oligomer with two or more (meth)acryloyl groups [oligomer (A) in the '658 patent] which does not result in a random distribution of (meth)acryloyl groups.